A critical requirement in modern building construction is energy conservation. A particular problem in view of the extensive use of glass in modern architecture is a loss of heat from the building through glass surfaces. One solution has been the increased use of insulating glass units comprising basically two glass panels separated by a sealed dry air space. Sealed insulating glass units generally require some means of precisely separating the two glass panels. The spacers currently used are generally tubular channels of aluminum or some other metal containing a desiccant to keep the sealed air space dry.
A significant problem arises because the metal spacer is a much better heat conductor than the surrounding air space. This leads to the conduction of heat from the inside glass plate to the outside glass plate from where it is dissipated into the atmosphere. Further, there can result a differential dimensional change between the glass and the spacer causing stress to develop on the glass and on the seal which can result in damage to and the failure of the sealed glass unit.
There have been some attempts to use spacers made of polyvinyl chloride* rather than metal. This has, however, been unsuccessful because the sealants which have been developed to construct reliable units bond well to glass and metal spacers but not to polyvinyl chloride spacers; this leads to structural weaknesses in units constructed with PVC spacers. Furthermore, the differential dimensional change that occurs between glass and PVC spacers over a certain range of temperature is much higher than with a metal spacer. In addition, most plastics have been found unacceptable for use between glass panes because they give off volatile materials, e.g. plasticizers, which cloud or fog the interior glass surface. FNT * See "Factory-Sealed Double-Glazing Units," Solvason et al, Canadian Building Digest, October, 1963.
The prior art does show some examples of the use of plastic over another core material, but the details of construction and environment differ entirely from the present invention. U.S. Pat. No. 3,694,985, for example, shows a wooden mullion element covered with a plastic extrusion, but this is not a spacer for double insulated glass. U.S. Pat. No. 3,070,854 shows a plastic channel member provided to cover a wooden separator between a pair of glass panes and U.S. Pat. No. 2,239,517 shows a metal separator provided with a plastic coating used in window construction. Again, the details of these devices are totally different than the present invention.
My own U.S. Pat. No. 3,918,231 shows an extruded plastic element for fitting over a metallic frame element. Also, my own U.S. Pat. No. 3,442,059 shows the use of a plastic spacer in the form of strips which fix into grooves provided in extruded metal holders for window panes, but this does not suggest the provision of a spacer having such plastic elements interposed between it and the window pane. Finally, U.S. Pat. No. 3,455,080 also shown plastic strips for holding window panes.
As indicated above, none of these prior patents is concerned with the particular problems of double insulated glass and none provides a solution to these problems.